Cardiac arrhythmias are the leading cause of death in the United States. Normally, electrical acquisition signals are conducted in an orderly way through the atrium and into the ventricle, passing each point in the heart only once in each heart cycle. Electrical acquisition signals at different locations in the heart are well correlated, taking into account normal propagation delays from one region of the heart to another. In response to local activation signals, the atrial muscle fibers contract in proper synchrony to pump blood through the atrium.
The electrical conduction system of the heart provides the rhythm, or sequence of contraction of the heart muscle, so it may most efficiently pump blood to the rest of the body. Electrophysiologists study the conduction system to diagnose and treat abnormal heart rhythms, known as arrhythmias. It is desirable to provide methods and equipment that assist physicians with diagnosing abnormal heart rhythms, as well as gauging the success of treating these arrhythmias through ablation therapies.
While it is not important to fully understand all the nuances of the field of cardiac electrophysiology, understanding the benefit of this invention does require a basic understanding of how the heart's electrical conduction system works and how some of these arrhythmias are treated.
Cardiac tissue, as it relates to the heart's electrical conduction system, has several important properties. First, a cardiac cell can receive electrical stimulus. Next, it can respond to this stimulus or activate. In the case of cardiac cells, they contract, causing the heart to squeeze and pump blood. In electrical terms, this activation is referred to as depolarization. It is a chemical process in the cell. Once depolarized, the cell needs time, a few milliseconds, to recover. During this repolarization phase, the cell is said to be refractory, meaning it has not fully recovered and cannot yet receive another stimulus. Finally, cardiac cells can propagate that electrical signal; that is, once stimulated, they can in turn stimulate the cells next to them. So, cardiac cells are activated sequentially from an initial point of stimulation, propagating outward, across the heart chamber. The refractoriness of cells just stimulated keeps the wave of depolarization from moving backwards; thus the wave continues forward across cardiac tissue or wall of a heart chamber in an organized fashion. The “pebble-in-a-pond” analogy is often used to describe this; the ripples move outward in an orderly manner from a singular point of stimulation. To build on this, note that, in the heart, some anatomical structures, such as heart valve openings and vessel ostia, will form obstacles for the wave of depolarization to navigate. Also, scars from cardiac surgery or damaged heart muscle do not conduct either, and the wave must make its way around the outside edge of these as well. In the pebble-in-a-pond example, one can imagine scars and heart valves as large rocks protruding from the pond surface; the ripples navigate round them and meet on the other side. That point of stimulation in a normal heart is made up of cardiac cells that have an additional property called automaticity. The chemical makeup of these cells allow them to stimulate themselves—thus starting the wave of depolarization—and then stimulate themselves again and again at a certain pace. Regular cardiac cells not have this property, so once repolarized and ready, they must simply wait to be stimulated again each time. This continual depolarization and repolarization keeps the heart beating at a regular rate, which is regulated to meet the need the oxygen demands of the body.
In a more macro sense, the heart itself has some features that allow it to depolarize and contract to pump blood in an organized and efficient manner. As shown in FIG. 1, a normal heart beat with a normal electrical pathway (NEP) starts at the Sinoatrial Node near the top of the right atrium (it is the SA node that has those cells with automaticity) and propagates across the right and left atria, causing them to contract and fill the ventricles with blood (a series of one-way valves in the heart prevents the blood from flowing backwards). The upper and lower chambers are divided by the atrioventricular septum which is made of membranous tissue that does not conduct electrical signal. Thus, the wave of depolarization cannot, in a normal heart, simply continue straight across from the atria to the ventricles. This is regulated by tissue at the one electrical channel connecting them. This collection of cardiac cells, called the AV node, has additional properties that cause it to delay depolarization, allowing the atria to completely contract. It then sends the electrical signal straight to the ventricle apices where the wave of depolarization across the ventricles results in an efficient contraction that sends blood to the lungs and the rest of the body. The delay between the atrial and ventricular depolarization causes the distinct “lub-Dup, lub-Dup” sound of the heart.
Electrophysiologists use electrode-tipped catheters placed at various locations in the heart to study its electrical conduction system in order to diagnose cardiac arrhythmias. They generally use well-established methods. The catheters are long thin, plastic tubes with wires inside running to a series of evenly-spaced electrodes or, more commonly, pairs of electrodes at the distal end which are used to record the local activation at that discreet location in the heart. When in contact with the heart wall, a pair of electrodes close together will measure just the electrical activity at that small piece of tissue. A recording system processes these electrograms and displays them on a monitor in real-time and also allows the user to freeze and review them. This allows the user to measure and compare the difference in timing of all the electrograms from the various locations at one moment in time in order deduce the current activation sequence and make a diagnosis.
Multipolar catheters, often with five or ten electrode pairs, are very helpful in analyzing a wave of depolarization across a particular piece of tissue. When such a catheter is positioned against the endocardium (the inside wall of the heart) so that it is oriented along a wave of activation, the delay in activation from one end to the other (distal-to-proximal or proximal-to-distal) will result in a slanted pattern of electrical activations. In FIG. 2A, the wave of depolarization crosses poles 1-2 of this catheter first. A few milliseconds later it crosses electrodes (or “poles”) 3-4, then 5-6, and so forth, all the way to poles 19-20, which it crosses last. On this catheter, poles 1-2 are said to be “earliest,” and poles 19-20 are said to be “latest.” FIG. 2B shows the resulting electrograms. For each heartbeat, or cardiac cycle, the electrogram of poles 1-2 are earliest on the timeline, with poles 2-3 deflecting a few milliseconds later and poles 19-20 the latest. Similarly, it is understood that a wave of depolarization moving in the other direction that crosses poles 19-20 first, followed by poles 17-18, 15-16, and so forth to poles 1-2, wherein poles 19-20 are earliest and poles 1-2 are latest, the visual pattern would be formed by electrograms slanting the other way. Mappings systems, discussed later, describe the timing of electrical activation as a graphical representation in terms of a color scale, where red represents earlier activation and purple represents later activation.
When the multipolar catheter is oriented across the wave of activation, or if there are two intersecting waves of activation, however, the electrograms will have a convex or concave visual pattern to them. In FIG. 3A, the wave crosses the distal and proximal poles 1-2 and 19-20 first, simultaneously, and passes poles 9-10 and 11-12, in the middle, last. The electrograms in FIG. 3B reflect this and form a concave visual pattern. Similarly, with a reverse situation, where poles 9-10 and 11-12 are crossed first and poles 1-2 and 19-20 are crossed last, the resulting electrograms' visual pattern would show a convex curve, as shown in FIG. 3C, with poles 9-10 and 11-12 early and poles 1-2 and 19-20 late.
Additionally, there is also a growing variety of special-purpose electrode catheters available. They can produce electrogram patterns that are much more complex and therefore difficult to interpret by electrogram pattern alone, as shown in FIGS. 4A and 4B.
In practice, the use of electrograms to diagnose arrhythmias requires a comprehensive understanding of the heart's anatomy as well as a clear knowledge of a catheter's current position in the heart chamber. Should a physician place the catheter in a different location than he or she thinks, or if it should dislodge after being placed in the correct location, the information provided by its electrograms will be inaccurate, leading to delays or even missed or incorrect diagnoses.
Arrhythmias, in general, can be categorized broadly as focal, reentrant, or disorganized. Focal arrhythmias have a single point of origin. A small group of cardiac cells away from SA node has gained the property of automaticity and depolarize at a fast rate. Since they activate faster than the SA Node, the cells there do not depolarize on their own; the SA Node is “suppressed”. Atrial Tachycardia is an example of this. The goal of therapy for this type of arrhythmia is to locate this group of cells depolarizing on their own and deliver localized RF energy (via the tip of an ablation catheter positioned at the site) to “ablate” or destroy them.
Reentrant arrhythmias, in contrast, do not have a single point of origin. The properties of depolarization, repolarization, and refractoriness, can enable a situation where the driving activation pattern forms a loop around a neutral, non-conducting structure such as a heart valve or surgical scar. Once initiated, the wave of depolarization takes it around the neutral structure, either clockwise or counterclockwise, in a circle. Although the wave of depolarization returns to tissue that had just activated as it made the previous loop, that tissue is now past its refractory period and is ready to be stimulated again, in this case by the return wave. The arrhythmia continues on this way, around and around, indefinitely. Atrial Flutter, for example, is a very common reentrant arrhythmia revolving around the tricuspid valve in the right atrium. The therapeutic strategy for reentry is to ablate a line of tissue (again, by means of an ablation catheter) from the neutral structure in the center of the loop to another, nearby neutral structure, thus creating a non-conducting lesion or “line of block” that disrupts the arrhythmia.
While electrograms provided by positioned catheters are helpful in diagnosing an arrhythmia, more precise information is often needed to fully understand the abnormal activation pattern and target the appropriate area for the therapeutic phase of the study, which commences after the diagnosis is made. In many cases, a detailed sampling of electrograms over much or all of the endocardial surface of one or more heart chambers is required.
Electroanatomic mapping systems have been developed to (1) clearly define the endocardial anatomy as a 3D virtual model, (2) record and catalog sampled electrograms, (3) display the activation sequence (or other data) compiled from recorded electrograms on the virtual model, (4) track and display in real-time the current location of electrode catheters in the heart by projecting accurate representations of them into the virtual environment, and (5) record precise locations of sites of interest such as places where RF energy has been applied.
In this two-step procedure—mapping followed by ablation—electrical activity is sensed and measured by advancing a catheter containing one or more electrical sensors into the heart, and acquiring data at a multiplicity of points. These data are then utilized to select the target areas at which ablation is to be performed.
Mapping of the heart or a region thereof typically involves using a mapping catheter with tip and proximal electrodes to record electrical activity in the region of interest. The catheter is moved along the wall of the endocardium during which precise locations and their corresponding electrograms are recorded. Through acquiring new points the three-dimensional anatomic map is created or developed in real-time.
Using the recorded electrograms, local activation times (LATs) are calculated relative to a body surface ECG or a fixed reference catheter. The LAT of each point is the interval between the beginning of the local electrogram of the mapping catheter and the reference signal. Importantly, because points are acquired during the same cardiac rhythm with the identical cycle length, and because the reference catheter or electrogram always remains fixed, the accumulating number of sampled locations and times can be compiled in real-time to accurately describe the activation sequence of one cardiac cycle or heartbeat. The LATs are described in terms of color—red representing the earliest activation so far recorded and purple representing the latest—and applied to an anatomical map of the region of interest to create an activation, or LAT, map. Each new acquisition, or “point,” updates the map until a complete—or at least sufficient—understanding of the activation sequence is presented.
FIG. 5 shows a series of new LAT as they are added to a map. Note that the anatomy has already been defined in this example and that the colors update as new data is recorded. The final image shows that a single focal site of activation has been located near the top of the chamber. A sample completed LAT map of Atrial Flutter is shown in FIG. 7A. The red-to-purple color pattern forms a clockwise loop around the tricuspid valve annulus (outlined by a green border), which has been cut out of the map. In this example, the mapping/ablation catheter shown in white, two additional electrode catheters in a darker green, and the site of ablation shown as brown circles, are also visualized.
Additionally, a completed LAT map can be visualized as a “propagation map” where the activation sequence on the map is played by the mapping system as an animation, showing the spread or propagation of electrical activation across the mapped region of interest each time it repeats. This can be a very helpful, dynamic alternative to visually following the rainbow scale of activation around a static LAT map where very slight, yet potentially important changes in color shade, may be missed. FIG. 6 shows a series of screen captures from a propagation map animation of the focal activation sequence shown in FIG. 5. In the animation, the wave in color red of depolarization moves in time across the chamber shown in color blue. Generally, the animations loop continually so the wave can be studied again once it plays through.
During the mapping phase, various parameters may be selected and thresholds set depending on the needs and desires of the electrophysiologist. For example, a “window of interest” (WOI) for assigning activation times on the mapping catheter is selected. This is a time interval relative to an electrogram of a catheter in a fixed location or body surface that has been chosen as “timing reference.” Only those activation times falling within this window are acquired. Thus, the WOI serves to limit the choice of electrograms to be measured to only those of the current heartbeat or cardiac cycle. A WOI too wide might include the next or previous cycles. The WOI can also be used in certain situations to exclude extra recordings on the mapping catheter electrogram such “stimulus artifact” from a pacing device, or “farfield signals”, including electrograms from another chamber or region that have been detected by the mapping catheter.
Each time a point is acquired, the system searches for an electrogram on the mapping catheter channel within the WOI. A time interval (in milliseconds) between the detected electrograms and the electrogram of the timing reference is calculated. This is recorded as the LAT or local activation time of that point. As the mapping catheter is moved and samples different locations, the timing of these locations varies with how early or late the wave of depolarization crossing the catheter at each particular location is, while in the current heart rhythm. So, the electrograms appear earlier or later compared to those of reference catheter, which remains fixed and, therefore, has the same timing of its electrograms every beat. For this reason, the LATs measured at each new point varies. The points with the lowest, or most negative, LATs are considered earliest and appear in colors red and orange on the LAT map; conversely those with higher or less-negative activation times are later and shade their areas of the map in colors blue and purple. It is the concept of the fixed reference catheter and its “timing reference” that allows the mapped points of many different heartbeats with the same activation sequence to be compiled into a comprehensive LAT map showing the activation sequence of one representative cardiac cycle.
These well-established, highly accurate mapping systems have been developed based on magnetic field sensing. They utilize sensors affixed to the catheter tip to measure the relative strengths of externally-generated magnetic fields and to derive from these measurements the location and orientation of the catheter which are used to very accurately display the distal ends of such “sensor-based catheters” and to create the 3-D anatomical maps representative of the region of interest. Methods for magnetic-based position sensing are disclosed, for example, in U.S. Pat. Nos. 5,391,199, 5,443,489, and 6,788,967 to Ben-Haim, in U.S. Pat. No. 6,690,963 to Ben-Haim, et al., in U.S. Pat. No. 5,558,091 to Acker et al., in U.S. Pat. No. 6,172,499 to Ashe, and in U.S. Pat. No. 6,177,792 to Govari, the entire content of each of which is incorporated herein by reference.
The mapping system may also include visualization of “non-sensor-based catheters” present in the region of interest. Such catheter visualization may display localized electrodes of those catheters, wherein “localization” (location/position detection of electrodes) is obtained through impedance or current-based measurements. For example, impedance is measured between electrodes affixed to the catheter and electrodes placed on the body surface. The position of the catheter and its electrodes is then derived from the impedance measurements. Methods for impedance-based position sensing are disclosed, for example, in U.S. Pat. No. 5,983,126 to Wittkampf, in U.S. Pat. No. 6,456,864 to Swanson, and in U.S. Pat. No. 5,944,022 to Nardella, the entire disclosures of which are incorporated herein by reference.
To summarize, there are two means of visualizing catheters present within region being mapped. Sensor-based catheters use sensors inside the catheter tip to measure the relative strengths of externally-generated magnetic fields and triangulate the location and orientation of the catheter. In contrast, the location and orientation of non-sensor-based catheters are derived from current or impedance measurements between the catheter's own electrodes and externally placed electrodes. The CARTO 3 mapping system, available from Biosense Webster, Inc., employs a hybrid technology of both the magnetic location sensing and current-based data to also provide visualization of both sensor-based and non-sensor-based catheters and their electrodes. The hybrid system, called the Advanced Catheter Location (ACL) feature, is described in U.S. Pat. No. 7,536,218 to Govari et al., the entire disclosure of which is incorporated herein by reference. FIG. 7A is a sample activation map generated by the CARTO 3 mapping system of a right atrium RA of a patient's heart, with visualization of three localized catheters.
The ACL technology is responsive to movement of the electrodes of the catheters and therefore updates the image of the electrodes in real time to provide a dynamic visualization of the catheters and their electrodes correctly positioned, sized, and oriented to the displayed map area on the CARTO 3 mapping system. The catheter visual representations therefore respond to being repositioned by the physician, dislodging from position, and subtler movements such as those caused by the patient's own breathing pattern. This dynamic movement of the catheter images stands in contrast to the 3-D maps themselves, which are created from a set of recorded locations and are, thus, static.
Originally, only the XYZ location of the data points could be used to create and refine the geometry of the chamber being mapped. Called “point by point” mapping, an electrophysiologist would “build out the shell” as he acquired more and more points. More recently, Fast Anatomical Mapping (FAM), a feature on the CARTO 3 mapping system, permits rapid creation of anatomical maps simply by the movement of a magnetic location sensor-based catheter throughout the cardiac chamber. The electrophysiologist can create the 3-D anatomical “shell” of the region of interest as rapidly as he can move the catheter along the wall of the heart chamber, and the electrical activation data may be acquired either simultaneously or after shell creation to create a 3-D electroanatomic map color coded to reveal its electrical activation sequence (or other data). The process of building a map—maneuvering the mapping catheter to numerous locations in the heart chamber to sample the electrical data there—takes time. Sufficient maps of simple arrhythmias can be made in just a few minutes, but more complex arrhythmias may require detailed maps that may take fifteen to thirty minutes or more to create. If the arrhythmia changes or is disrupted, the activation sequence is no longer the same, so new data cannot be added to this map. The electrophysiologist may choose to “remap,” in which case the geometry only of the current map is copied to a new map file and new data points in the new heart rhythm may be acquired to color in this “blank canvas.” Depending on the size of the region of interest, remapping may take as long to create as the original map, as the sensing catheter is moved from location to location to acquire a new set of LATs.
For the simpler arrhythmias, the electrophysiologist may choose not to remap but merely refer to the electrograms of properly positioned multipolar catheters (for example, see FIGS. 2B and 3B), which, as mentioned earlier, are typically displayed on a recording device during an ablation procedure to provide additional data for use by the electrophysiologist. Electrograms may be particularly informative for those regions or chambers of the heart where there are well-established, standard catheter positions as well as established ablation patterns. An atrial flutter ablation procedure is one of the simplest examples of this. As briefly mentioned earlier, reentrant signals of atrial flutter in the right atrium typically have a circuitous path that is clockwise or counterclockwise around the tricuspid valve annulus TVA. FIG. 7A shows a map of clockwise atrial flutter created using FAM and a dual-purpose, sensor-based mapping and ablation catheter. The red-to-purple color pattern in this map can be traced clockwise around the valve (center circular cutout with thin green border) from the red area in the upper corner all the way around in a loop to the purple area returning to the starting point (CARTO 3 places the brown “early meets late line” into the map automatically between red and purple points). Only one cardiac sequence is described by the map; in reality the wave of depolarization continues around and around in a continuous loop around the TVA. In FIG. 7A, three catheters are visualized. Catheters for this procedure typically include a nonmagnetic, current-based sensing “Duo-deca” multipolar catheter (in green) that enters the right atrium RA from the IVC and is generally positioned in a loop just outside the TVA. Its electrograms, therefore, help describe how the electrical activation is moving around the tricuspid valve. Longer versions of this catheter (actually, ones with more widely-spaced electrode pairs), like the one pictured, can extend across the floor of right atrium (the cavotricuspid isthmus) and into the coronary sinus ostium. A properly positioned Duo-Deca catheter produces a very distinct “slanted” electrogram patterns in atrial flutter (see for example, FIG. 2B). The direction of the slant indicates whether it is clockwise or counterclockwise atrial flutter (for example, clockwise in FIG. 2B). Also visible in this map is the distal tip of a nonmagnetic, current-based HIS catheter (in green) protruding through the TCV from the right atrium RA into the right ventricle RV, and, of course, the magnetic sensing mapping and ablation catheter (in white), shown protruding from the IVC at the cavotricuspid istmus.
The typical ablation pattern for treating atrial flutter is an ablation line across the cavotricuspid isthmus CVI (at the floor of the heart), forming a “line of block” between the tricuspid valve TCV and the inferior vena cava IVC. The map in FIG. 7A shows this as well, as brown circles on the floor of the heart marking ablation sites. When the CVI is ablated, the flutter terminates and the patient's normal heart rhythm will resume. However, it is still necessary to confirm that the ablation line is truly complete because the flutter may terminate when the tissue is merely damaged and not yet truly ablated. This is done by pacing (delivering external electrical stimulus) from a catheter positioned just to the side of the ablation line and observing the resulting activation sequence via the DuoDeca's electrograms. This can also be accomplished by “remapping” the new activation pattern by acquiring new activation points around the valve while still pacing. Here the electrograms' visual pattern will either be a slanted line indicating the line of block is complete and the wave of activation must travel all the way around the valve to depolarize the tissue on the other side of it, or a curved line which suggests that, in addition to traveling up and around the valve, a wave of depolarization is also moving right across the ablation line. The latter reveals there is still more tissue left to ablate to form a complete line of block. FIG. 7B is a map of the same procedure, made during pacing to demonstrate a complete line of block. The pacing stimulus is being delivered to an electrode pole just to right of the ablation line in the color red area of the map. One can trace the resulting activation sequence by following the colors of the rainbow in sequence (red, orange, yellow, green, blue, and purple) starting with red and moving up and around the valve in a counterclockwise fashion all the way to the purple area just to the left of the ablation site, which is the latest tissue activated in the chamber during this pacing maneuver. The map indicates that the line of block is indeed complete. The electrograms of the Duo-deca catheter, from the proximal poles to the ones just leftward of the ablation line would have a slant pattern similar to those shown in FIG. 2C.
FIGS. 8A and 8B show another example of using the same pacing maneuver to confirm that the ablation line in the CVI is complete. Note the activation pattern in FIG. 8A, where the wave of depolarization, as evidenced by the red-to-purple color pattern of the map, shows activation moving from the red area (at the lower right of the map) not only up and around the top of valve, but also across the ablated line and the floor of the heart, as indicated by the green areas both at the roof and to the left of the ablation line. The latest area of activation in purple is the far wall (at the left of the map). This “split” evidenced by two different green areas shows that there was not a complete line of block and that more ablating was necessary. The electrograms on a duo-deca catheter in this situation would reveal a distinct curved pattern to the electrograms (as shown in FIG. 3B), with both the proximal and distal poles activating earlier than the middle poles. More RF energy was delivered and another remap, FIG. 8B, was again created while pacing to the right of the line. This map clearly shows that now the line of block is complete.
It is not uncommon for an ablation procedure to require several rounds treatment alternating between ablation and pacing for block assessment before the line of block is deemed completed and successful. If remapping is performed for each block assessment with each remapping for a new set of LATs each taking 5-10 minutes to create, these repeated remappings can greatly lengthen the duration of the ablation procedure. Thus, in the treatment of atrial flutter in the right atrium, for the reasons discussed above, the electrophysiologist may merely rely on the electrograms after each round of ablation without remapping to assess the block It should be noted that one of the understated benefits of using a mapping system is that catheters are visualized without the need of ionizing radiation. Using only fluoroscopy requires that the patient be exposed to radiation to position catheters and continually check their location. In a long procedure, this can add up.
Electrograms of a successful block at the isthmus reveal one or more diagonal lines, each having the same or similar slope, such as item D in FIGS. 9A and 9B. However, electrograms of breakthroughs through incomplete blocks often reveal two diagonal lines with opposite slopes which form either a convex or concave shape depending on the location of the pacing signal, such as items D1 and D2 in FIGS. 9C and 9D. The electrograms in FIG. 9A describe the electrograms generally expected when pacing from the right side of a complete ablation line as in FIGS. 7B and 8B. The concave shape of the electrograms in FIG. 9D, however, indicates the situation in FIG. 8A, where the line of block is not complete (FIGS. 9B and 9C show pacing from the left side of the line, which is occasionally done as well to confirm block from both sides, or “bidirectional block”). FIGS. 10A-10D schematically represent the right atrium with anatomical features of the coronary sinus CS, the superior vena cava SVC and the inferior vena cava IVC. These figures illustrate the locations of the catheters CT and the paths P of the respective electrograms of FIGS. 9A-9D. In FIGS. 10A and 10B, the earliest activation site S and the ablation line A are also shown. In FIGS. 10C and 10D, the breakthrough due to an incomplete ablation line B is shown.
It is understood that the DuoDeca catheter shown in FIG. 7B has more widely-spaced poles—giving a longer span of coverage—than other catheters of the same type. This catheter sits with its poles 1-2, 3-4 and 5-6 actually across the ablation line. While the electrograms in FIG. 9A-9D represent a more standard catheter with all the distal poles positioned to the left of the line, the electrophysiologist will have to know and consider the anatomical location of each catheter and its electrodes when analyzing the EGM pattern. The precise electrogram pattern for situation in FIG. 7B is shown in FIG. 11. Here, activation of poles 1-2, 3-4 and 5-6 (L1), is much earlier because they are on the right side of the ablation line, closer to the site of pacing. The straight, slanted line pattern (L2) made by from poles 19-20 to 7-8 shows the counterclockwise activation up and around the tricuspid and ending at the left side of the line, thus confirming block.
Because experienced electrophysiologists can usually recognize at a glance the electrograms of FIGS. 9A and 9B as complete lines of block, and those of FIGS. 9C and 9D as incomplete lines of block for atrial flutter, they may rely on the electrograms only and chose not to remap after each ablation treatment in order to avoid unnecessarily lengthening the duration of the ablation procedure. However, it would be desirable to provide another means by an electrophysiologist can readily confirm his reading of the electrograms without the need to refresh the activation map. It would be desirable to provide visualization of such other indication of the LATs and/or electrode activation of the catheter for easy reference by the electrophysiologist, and further to provide such visualization on an existing display that is already referenced by the electrophysiologist.
Such desirable features would be particularly advantageous in the diagnosis and treatment of atrial fibrillation (AF), a well-known disorder of the heart, which causes hemodynamic efficiency to be reduced and, in serious cases, can lead to cardiac embolization, stroke, ventricular arrhythmias and other potentially fatal complications. AF can arise from aberrant signals entering the left atrium via the pulmonary veins connected to it. A very common, but rather technically challenging, treatment for AF is a pulmonary vein isolation procedure (PVI), where the cardiac tissue around the ostia of each of the four pulmonary veins in the left atrium is ablated to create a circular line of block preventing these aberrant signals from entering the chamber. Though there are numerous variations of a pulmonary vein isolation employed by electrophysiologists, the common goal is the same. FIG. 12 shows typical left-atrial anatomy with the four pulmonary veins shown in bright colors yellow (right superior), orange (right inferior), purple (left superior) and pink (left inferior). The red structure is the left atrial appendage. Also visualized is the tip of the mapping/ablation catheter as well as brown “point tags” marking ablation sites near the left superior pulmonary veins.
Due to the tubular structure of pulmonary veins, specially-shaped circular mapping catheters (such as Biosense Webster's Lasso catheter, shown visualized by the CARTO mapping system, in FIG. 13) are typically used in the pulmonary veins to analyze electrograms before, during and after ablation procedures. Due to the technical challenges associated with LAT mapping inside the PV, and the fact that the activation sequence changes continuously as more of the tissue is ablated, electrophysiologists almost universally rely on analyzing the Lasso electrograms on the recording system rather than mapping and remapping each change.
As shown in FIG. 13, a lasso catheter (in royal blue) can sit with its distal loop in a pulmonary vein (represented by pink “webbing”) with its electrodes in contact with an inner circumference of the vein. The lasso catheter is visualized in an anatomical (anatomy only) CARTO map of the left atrium (the veins have been made transparent by the “webbing”). Other catheters and pink dots marking the current progress of the ablation are also visible. Typically, the size or diameter of the distal loop is adjusted so that the loop and electrodes make adequate contact along the entire inner circumference of the vein in order to sense any aberrant or pacing signals that pass the loop traveling from the LA into the vein or from the vein into the left atrium usually in normal sinus rhythm. Three-dimensional mapping with hybrid localization technology reveals the position of the catheter distal loop and electrodes. However, technical considerations may cause the distal loop to be positioned randomly with its distal and proximal electrodes in any radial orientation. Additionally, since pulmonary veins vary greatly in size, changing the loop diameter to fit properly will also change the association of the loop's distal and proximal electrodes—poles may overlap in small veins or there may be a gap in large veins. FIG. 13 is an example of overlapping electrodes on the lasso catheter. For these reasons, the electrograms alone may reveal which pole(s) are acquiring and the sequence of acquisition but not how this actually correlates to the anatomy itself. For this, the electrophysiologist must cross-reference the electrograms with the 3-D map and the visualized Lasso catheter in order to ascertain the location of acquiring pole(s) relative to the anatomy and hence the location of breakthrough(s) in the ablation line for placement of the ablation catheter.
Although the procedure is a treatment for AF, it is usually performed in normal sinus rhythm to help better gauge the success of lesion formation. As the ablation of tissue around the pulmonary vein ostium proceeds, the electrogram pattern will change on the lasso catheter. In general, the sections that have yet to be ablated will have earlier corresponding electrograms. The ablation of a pulmonary vein is complete when the wave of depolarization across the heart chamber (in the patient's normal heart rhythm) is blocked from entering the vein, and electrograms disappear completely from the Lasso catheter sensing from inside the vein. This process is repeated for each of the four pulmonary veins.
Due to the technical challenge of positioning the mapping/ablation catheter with sufficient contact to create durable lesions at each location around each pulmonary vein ostium, multiple ablations at the same locations are frequently required, and continual analysis of the Lasso electrograms is critical. The electrograms are studied on the recording system to determine the electrode to target, and then those electrodes are located on the visualized lasso catheter in the map.
Mapping systems are very useful for this procedure. Knowledge of each patient's particular anatomy, and especially the orientation and position of the catheters inside it, are crucial. Marking sites of ablation is also very important. However, activation mapping is rarely done. This is because the activation sequence inside each pulmonary vein continuously changes while ablating, and this renders any map made useful for only a brief period of time before a remap is required.
In addition to the changing activation sequence, the Lasso catheter commonly falls out of position or gets dislodged while trying to maneuver the mapping/ablation catheter around in the same space. Repositioning it almost always results in a slightly or greatly different radial orientation than before, meaning its electrodes now represent a different location, and the electrograms and their corresponding positions in the map must be reassessed. For these reasons the following process must be repeated numerous times per procedure. First, once in proper position, the Lasso's electrograms are recorded and analyzed on the recording system. Next, a particular pole is named the current target for ablation. Then the electrophysiologist determines where that pole is located on the catheter image on the mapping system. Finally, he uses the mapping system to position the ablation catheter near that pole to ablate that tissue. After this RF application, as changes in the activation sequence on the Lasso are observed, the process is repeated. The questions, “what's early now?” and “where is that” might be asked several dozen times in a challenging case.
Once, again, it would be desirable to provide an improved means of visualization of the electrode activation of the catheter for easy reference by the electrophysiologist, and further to provide such visualization on an existing display that is already referenced by the electrophysiologist.
Recently, catheters with more complex shapes, such as Biosense Webster's PentaRay catheter shown in FIG. 4A, have become more common. Though helpful for creating LAT maps more quickly by taking multiple points at a time, the PentaRay's electrograms are very difficult to recognize by activation pattern alone (see, for example, FIG. 4B). Here as well, there is a need for this improved means of catheter electrode activation visualization.
Accordingly, there is a desire for a system and method for real-time visualization of electrode activation on a multi-electrode catheter, so a user can instantly recognize signal acquisition by electrodes, including a sequence of electrode acquisition, without reference to electrograms or a 3-D map or wait for any other information. The system and method need not consider any timing reference and may function independently of any mapping or acquisition/propagation maps of any mapping system. However, the system and method may provide visualization of electrode acquisition on a 3-D activation map with LATs information and catheter and electrode localization so that location of any and all acquiring electrodes relative to the mapped region is revealed.